A plasma antenna can be as simple as a glass tube containing a rarefied gas, such as argon. A simple fluorescent lamp or a neon sign can act as a plasma antenna under the proper conditions. Under non energized conditions, the tube does not appreciably interact with radio waves. However, when the rarefied gas is ionized to contain free electrons, it electrically behaves as a metal. It can transmit, receive, and reflect radio waves. When the gas de-ionizes, it reverts to the non interacting state.
The advantages of plasma antennas over metal antennas are several. The plasma antenna can be made to disappear electrically when the gas is not ionized. In this state it does not appreciably reflect radio waves, and so is very useful for stealth applications. The plasma antenna is reconfigurable. Several plasma antennas can be placed in the same space, and only the ionized one will be effective, transmitting through the non ionized plasma antennas. The plasma antenna can be operational at a lower frequency, while being transparent at a higher frequency. This is useful in electronic warfare, when a high frequency electronic warfare signal will pass through an plasma antenna that is operating at a lower frequency, without interacting with it.
The plasma antenna operates as efficiently as a metal antenna in both reception and low power transmission. Although the plasma antenna has several advantages over a metal antenna, it also has several problems. The highest frequency that has been used for direct current transmission is eight hundred megahertz. When the discharge current is increased to increase the electron density and the plasma frequency (electron density dependent), the electrodes burn out. Further, during the duration of the current flow, plasma instabilities occur, and generate unwanted noise. In addition, the discharge current requires about twenty watts for a relatively small antenna, and for a multi tube antenna, the power consumption is quite high.
What is needed, therefore, is a plasma antenna that overcomes problems such as those described above, at least in part.